The present invention relates to cementing operations and, more particularly, in certain embodiments, to cementing methods and compositions that comprise biowaste ash.
Cement compositions may be used in a variety of subterranean applications. For example, in subterranean well construction, a pipe string (e.g., casing, liners, expandable tubulars, etc.) may be run into a well bore and cemented in place. The process of cementing the pipe string in place is commonly referred to as “primary cementing.” In a typical primary cementing method, a cement composition may be pumped into an annulus between the walls of the well bore and the exterior surface of the pipe string disposed therein. The cement composition may set in the annular space, thereby forming an annular sheath of hardened, substantially impermeable cement (i.e., a cement sheath) that may support and position the pipe string in the well bore and may bond the exterior surface of the pipe string to the subterranean formation. Among other things, the cement sheath surrounding the pipe string functions to prevent the migration of fluids in the annulus, as well as protecting the pipe string from corrosion. Cement compositions also may be used in remedial cementing methods, for example, to seal cracks or holes in pipe strings or cement sheaths, to seal highly permeable formation zones or fractures, to place a cement plug, and the like.
Cement compositions used heretofore commonly comprise Portland cement, which is generally is a major component of the cost for the cement compositions. To reduce the cost of such cement compositions, other components may be included in the cement composition in addition to, or in place of, the Portland cement. Such components may include fly ash, slag cement, shale, metakaolin, micro-fine cement, cement kiln dust, zeolite, and the like. “Fly ash,” as that term is used herein, refers to the residue from the combustion of powdered or ground coal, wherein the fly ash carried by the flue gases may be recovered, for example, by electrostatic precipitation. “Slag,” as that term is used herein, refers to a granulated, blast furnace by-product formed in the production of cast iron and generally comprises the oxidized impurities found in iron ore. Slag cement generally comprises slag and a base, for example, such as sodium hydroxide, sodium bicarbonate, sodium carbonate, or lime, to produce a cement composition that, when combined with water, may set to form a hardened mass.
Large amounts of biowaste are generated worldwide each year. Biowaste ash can be derived from a number of sources including agricultural waste, municipal waste, waste-water treatment waste, animal waste, non-human-non-animal industrial waste, and combinations thereof. A number of different methods for disposal of biowaste have been developed, including application to surface land, composting, and landfill disposal. In addition, billions of tons of biowaste are burnt every year, resulting in tons of ashes that must be disposed.